Hi,
How are you powering all the LEDs?
Have you monitored the voltage level as you increase the number of LEDs ON?
Have you at anytime had more than 170 LEDS alight?
Have you swapped your strips around to make sure you do not have a faulty 2811 LED somewhere?
Can you post a diagram of how you have the LEDs connected to the power supply.
Are you feeding each strip directly back to the suppy or are you daisy chaining the power lead.
Don't forget that apart from the signal input line being essential, a good gnd return is also important as the signal reference needs to be stable, this gnd is also conducting the LED current.
If this gnd is not good, you will have a changing volt drop down the strip, this changing drop will effect your signal transmission.
Tom... 